The desire for improved ride control in motor vehicles has: lead to the development of “active” vehicle suspension systems. Such systems typically use sensors to sense the various ride characteristics of the vehicle, the sensors providing signals to an Electronic Control Unit (ECU). The sensors sense any excessive roll, pitch, four wheel bounce and warp motions of the vehicle and its wheels, and the ECU seeks to actively compensate for this motion by controlling the supply of high pressure fluid from a fluid pump to different actuators acting within the vehicle suspension system, or by controlling the return of high pressure fluid from the actuators to a fluid reservoir. (The warp mode of a suspension system, also known as cross axle articulation, is defined as when one pair of diagonally spaced wheels together move in the opposite vertical direction to the other pair of diagonally spaced wheels with respect to the vehicle body). Active suspension systems which attempt to control all the above-noted ride characteristics are very expensive and complicated and have therefore not proven to be commercially viable. Simpler active systems which only seek to actively control excessive roll motions of the vehicle have therefore also been developed. Similarly, adaptive damping systems are becoming popular as they can be used to influence vehicle motions such as roll, pitch and whole body bounce by changing the damping rates at each wheel without the need for a pump.
All the known active suspension systems however have a number of problems which have prevented commercial acceptance of such systems except in luxury vehicles. The number of components required for such systems have lead to packaging difficulties, with the limited space available for such systems under existing motor vehicles. The complexity of active suspension systems and the high stresses applied to certain components of the system lead to ongoing reliability issues. Furthermore, active systems typically require a large number of components, some of which are specially produced components that can handle high mechanical stresses leading to high manufacturing costs. Also, expensive high pressure and high speed components are typically used in such systems, resulting in relatively higher manufacturing and running costs for active systems when compared with conventional suspension systems. Another disadvantage of active systems is the poor response times generally associated with production feasible versions of such systems. Valves are generally used to control the fluid flow in the system. There is always a certain delay before a valve can be actuated to allow or prevent fluid flow. This delay, together with other delays caused by inadequately defined algorithms controlling the system, can lead to unacceptably poor response times for the active suspension system. Active roll control systems typically respond too slowly when undergoing a quick slalom test for example, the control system being unable to provide adequate control under large changes of inertia.
The Applicant has developed a number of different vehicle system systems which seek to avoid at least some of the problems associated with active suspension systems while providing substantial improvements in the ride of a vehicle. These systems are “passive” and do not require sensors, ECUs or fluid pumps to operate. Such systems are described in Australian Patents 670034, 694762, 671592 and 699388 and International Application No. PCT/AU97/00870, details of which are incorporated herein by reference. These systems do however generally rely on components adapted to handle high pressure fluid.
Adaptive damping systems have been developed specifically to improve the damping function of a vehicle suspension system. These damping systems only require relatively low pressure components when compared with those required in the previously described systems, but provide substantially no roll stiffness. They generally have electrically variable or switchable orifices and preloads which are controlled to provide more appropriate damper forces in a range of predefined conditions to avoid the compromises of a single setting to suit all conditions.
In U.S. Pat. Nos. 5,486,018 and 5,584,498 (Yamaha), there are described interconnected damper systems where the top chamber of at least one pair of laterally or longitudinally adjacent dampers, commonly known as Oshock absorbers' are connected by a conduit. A number of arrangements are disclosed, providing a range of damping effects. However, none of the arrangements are designed to provide a roll stiffness for the suspension.
In U.S. Pat. No. 4,606,551 (Alfa), there is described an arrangement having dampers, each having an upper and lower chamber. At least one pair of laterally or longitudinally adjacent dampers are connected by conduits respectively connecting the upper chamber of one damper with the lower chamber of the other chamber. A number of damper valves are provided in the connecting conduits to provide various damping effects. No electronic control is required, nor can the arrangement provide a roll stiffness for the suspension.
Although each of the above described adaptive and interconnected damping systems provide an improved damping function over conventional damper arrangements, they do not provide any or only provide minimal control of other ride characteristics of the vehicle. For example, none of the above adaptive or interconnected damping systems provide roll support for the vehicle as they do not have any roll stiffness to enable a degree of roll control for the vehicle, only roll damping. These systems can therefore not be used to provide roll control for the vehicle.